<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>回顾一个DOM操作</title>
  <style>
    .demo{
        background-color: orange;
    }
  </style>
</head>
<body>
<button id="btn">点我创建一个输入框</button>
<script type="text/javascript">
  const btn=document.getElementById('btn')
  btn.onclick=()=>{
    const input=document.createElement('input')
    input.className='demo'
    input.value=99
    input.onclick=()=>{alert(1)}
    document.body.appendChild(input)
    input.focus()
    input.parentElement.style.backgroundColor='skyblue'
  }

</script>
</body>
</html>